1. Field of the Invention
The present invention relates to a rotational phase adjusting apparatus used for, for example, valve timing adjustment which adjusts opening/closing timings (valve timing) of intake valves and exhaust valves of an internal combustion engine (engine) in accordance with engine operating conditions.
2. Related Art
In a conventional valve timing adjusting apparatus for adjusting valve timing of intake valves and exhaust valves of an engine, as disclosed in JP-A 5-214907 or JP-U 2-50105, a driving force is transmitted from a crankshaft as a driving member of the engine to a camshaft as a driven member through a driving force transmitting mechanism. The driving force transmitting mechanism may be a vane type in which vanes are accommodated relatively rotatably in a housing and the rotational phase difference of the vanes relative to the housing is adjusted by the fluid pressure of operating fluid.
In the apparatus according to JP-A 5-214907, a housing comprises a circumferential wall and a pair of side walls covering axial side ends of the circumferential wall. This housing having three constructional parts causes the following drawbacks.
(1) A seal is necessitated at the joint surface between the circumferential wall and the side walls to restrict the leakage of an operating fluid, resulting in the increase in number of the parts and enlargement of the outer diameter of the housing by a groove for receiving the seal between the circumferential wall and the side walls.
(2) The centers of the bearing parts of the side walls of the housing deviates from each other due to variations in the machining precision and in the assembling precision of the parts.
In the apparatus according to JP-U 2-50105, as opposed to the above apparatus, a circumferential wall and a gear side wall which form a housing are made integrally. This housing does not cause the above drawbacks. In this integral type housing, however, the diameter of the gear side wall is determined by the diameter of the circumferential wall. As a result, the gear side wall cannot be reduced in radial size. Further, in the case the circumferential wall and one side wall is formed integrally, the inner angled corner between the circumferential wall and the side wall is smoothed causing low sealing ability thereat. Still further, the material for the housing is limited with respect to its rigidity, strength and the like.
In the case that a seal 112 is disposed in rotating sliding part between a vane 110 and a housing 111 as shown in FIG. 11 to seal a fluid pressure chamber to which the operating fluid is supplied to drive the vane 110, a wear step 111a is likely to be caused on the housing 111 if the seal 112 has a higher hardness (wear-causing characteristics) than the housing 111. The wear step 111a appears at positions where the seal 111 slides more often. When the seal 112 slides and reaches the wear step 111a, the seal 112 receives the fluid pressure in the arrow direction A from the side of the housing 111 and may be pushed into the side of the vane 110. This causes the leakage of the working fluid between the fluid pressure chambers provided on both circumferential sides of the vane 111 and it becomes hard to hold the vane 110 at the position shown in FIG. 11. This local wear of the housing will disable the vane to be controlled and held at the intermediate position. Though it is possible to restrict the wear of the housing by using a hard material such as an iron, such a material will increase the production cost and the weight of the housing.